Deep-water marine caves are one of the Earth 's last largely unexplored frontiers of undiscovered fauna (animal life). More than 150 limestone caves are known to exist in or near the island of Bermuda. Many of these caves have extensive but relatively shallow submerged portions that connect to the sea via tidal springs along the coastline. These inland caves are inhabited by a number of diverse eyeless and colorless crustaceans and other invertebrates. Many of these organisms are "living fossils "; and some are most closely related to deep-sea organisms.